The present invention relates to subterranean operations and, more particularly, to apparatus and methods for simulation of bore hole fractures.
Drilling operations play an important role when developing oil, gas or water wells or when mining for minerals and the like. During the drilling operations, a drill bit passes through various layers of earth strata as it descends to a desired depth. Drilling fluids are commonly employed during the drilling operations and perform several important functions including, but not limited to, removing the cuttings from the well to the surface, controlling formation pressures, sealing permeable formations, minimizing formation damage, and cooling and lubricating the drill bit.
When the drill bit passes through porous, fractured or vugular strata such as sand, gravel, shale, limestone and the like, the hydrostatic pressure caused by the vertical column of the drilling fluid exceeds the ability of the surrounding earth formation to support this pressure. Consequently, some drilling fluid is lost to the formation and fails to return to the surface. This loss may be any fraction up to a complete loss of the total circulating drilling fluid volume. This condition is generally known in the art as “Lost Circulation.” Failure to control Lost Circulation increases drilling cost and can damage formation production capabilities.
The general practice is to add any number of materials to the drilling fluid which act to reduce or prevent the outward flow of the drilling fluid in a porous and or fractured stratum by sealing pores or cracks, thereby reducing or preventing Lost Circulation. The materials used in this process are commonly referred to as Lost Circulation Materials (“LCM”) and may be particles or polymers. Some materials typically used as LCM include, but are not limited to, wood fiber, popped popcorn, straw, bark chips, ground cork, mica, ground and sized minerals and the like.
Further, a technique generally referred to as wellbore strengthening (“WS”) may be used to effectively strengthen the walls of a wellbore to prevent fracturing due to overpressure and the subsequent Lost Circulation. This technique takes advantage of inadvertent fractures from normal drilling operations and deliberately induced fractures by sealing and propping the fractures open. Consequently, the wellbore wall is compressed and a higher pressure is required to cause new cracks and further losses of drilling fluid.
In order to optimize the efficiency of drilling operations, LCM may be used in conjunction with Wellbore Strengthening Materials (“WSM”). In some instances, the WSM particles may be larger than the LCM particles. It is desirable to be able to simulate the effect of LCM and/or WSM particles on the formation in order to improve the efficiency of drilling operations and identify the LCM and/or WSM particles best suited for a given formation and performance criteria. Specifically, it is desirable to be able to test a carrier fluid's ability to transport WSM or LCM particles into a new fracture. Further, it is desirable to be able to test the WSM's or LCM's ability to remain in the fracture and prop it open to induce wellbore stress in order to reduce Lost Circulation.